Consider using the eye-dropper tool set to a Sample Size of "5 by 5 Average" and select a spot extremely close to the tattoo's edge.
Then select your brush tool, set the brush to "Rough Round Bristle", Hardness around 20%, Opacity around 90%, Flow at 100%, Brush Size should be set to cover only a small portion of the tattoo, and then apply brush strokes on the part of the tattoo near the location you took the sample. Work in small strokes moving toward the center of the tattoo.

Repeat all of the above starting at a new location close to the tattoo's edge. Do this going around the tattoo, working from the outside edge towards the center.

This will bring in color tones and brightness values from different directions but with similar values. Then apply healing brush to the area. Evening the texture and tone of the tattoo area first will make any healing brush strokes and/or patching done after look better.

I sometimes change the opacity to 100% depending on how things look when I start this technique. I can get rid of a large or complicated tattoo in about 5 minutes this way. I am sure other techniques might be faster, but I have used this successfully for a long time and have grown accustomed to it.

I have a series of three images in my MM portfolio, the original, straight out of the camera, the second one where I redistributed the tones to my liking, and the third one where I painted out the tattoos and fingernails with a small paintbrush, on a separate layer, sampling colors from the surrounding areas. (the paintbrush becomes a sampling tool when you press the Alt key). When I got all the gradients and colors to "look perfect", I added a small amount of noise, then blur, then Edit>fade blur, to get the texture to match the skin texture perfectly. It is a sensitive process to make it absolutely undetectable, but worth the time and effort for my artistic purposes, (not good for high production purposes). The following are the results :
http://www.modelmayhem.com/portfolio/pi … 1#28549401 18+
http://www.modelmayhem.com/portfolio/pi … 1#28549441 18+
http://www.modelmayhem.com/portfolio/pi … 1#28549466 18+
-Don
EDIT: Oh, by the way, a Wacom tablet, with the tool set to pressure sensitivity, for opacity of the effect, is HIGHLY advisable.

GeorgeCrane wrote: @Don Garrett thanks for the reply. i don't have a tablet but been thinking about getting one as many people seem to praise them.

@Peano Sorry i should have been more specific, i did mean about improving them.

I totally interpreted your post as asking HOW TO GET RID OF THEM. After rereading it, and along with your clarification above, I see that was almost certainly a wrong interpretation. Anyway, I hope someone has benefited from my response. I'll reiterate, a Wacom tablet is absolutely indispensable in my process.
-Don

For small tattoos the patch tool will work well to get rid of them. For larger ones, or ones where there is not enough exposed skin nearby the tattoo, you will have to resort to the clone tool and then blurring the lines with the patch tool.

The simplest way to solve it is to do what I do. I simply don't bother with models whose tattoos I cannot remove in less than a minute or two with the patch tool. There are usually no shortage of models to go around.